“It’s a tragedy of the worst kind,’ Mayor de Blasio says Wednesday
near Park Ave. and E. 116th St. Up to 10 people were still missing
from the two buildings that contained 15 apartments, Absolute Piano
and Spanish Christian Church, an NYPD source said. One of the
victims was identified by sources as Griselde Camacho, 44, who lived
at 1644 Park Ave.”

Nobody knows for sure the cause, but it appears to be gas:

“There was no warning in advance,” said Mayor de Blasio,
who added that the cause of the blast that also flattened 1646 Park
Ave. appears to be a gas leak.